Hollow blade construction



Jan. 16, 1962 T. FOSTER ETAL HOLLOW BLADE CONSTRUCTION 4 Sheets-Sheet 1INVENTOREI TEIM FDEITER WERNER E. HIJWALD M ATTDBLNEY F iled Nov. 23,1956 Jan. 16, 1962 T. FOSTER ETAL HOLLOW BLADE CONSTRUCTION 4Sheets-Sheet 2 Filed NOV. 23, 1956 JNVENTOREI v TDM Fun-ran WERNEREL'HDWALD ATTORNEY T. FOSTER E' l'AL HOLLOW BLADE CONSTRUCTION Jan. 16,1962 Filed Nov. 23, 1956 INVENTOREI TEIM FD ER WERNER E.HD

ATTORNEY 4 Sheets-Sheet 3 Jan. 16, 1962 T. FOSTER ETAL HOLLOW BLADECONSTRUCTION 4 Sheets-Sheet 4 Filed Nov. 25, 1956 'lll'llll'lll s ,0 o aa o a 6 9 O O G V EN TOR: T M FEISTER D M w .u H v E R E N R E wATTORNEY 3,017,159 HQLLOW BLADE CQNSTRUCTIGN Tom Foster and Werner E.Howalrl, Ridgewood, N.J., as-

signors to Cnrtiss-Wright Corporation, a corporation of Delaware FiledNov. 23, 1956, Ser. No. 623,943 3 Claims. ((31. 253-3915) This inventionrelates to hollow blades for turbines, compressors or the like and isparticularly directed to such blades designed for the flow of heatexchange fluid therethrough.

object of the present invention comprises the provision of a novelhollow air-cooled blade for turbines, compressors or like apparatus suchthat high cooling efficiency of the blade is provided. A further objectof the invention comprises the provision of a hollow air-cooled blade inwhich the blade is provided with a plurality of passages each controlledby a restricted discharge orifice disposed along the trailing edge ofthe blade. With this arrangement, the cooling air passages all dischargeinto the surrounding fluid in a region of substantially known pressurevelocity and temperature thereby permitting accurate control of thecooling air flow through each passage. Also because of the restricteddischarge orifices the cooling air discharges from the blade trailingedge at high velocity thereby insuring good cooling at the normally hotblade trailing edge. Furthermore, by properly proportioning the relativeareas of the restricted discharge orifices of saidblade passages anydesired distribution of relative magnitudes of the mass air flow throughthe blade passages can be obtained. Thus with the present invention itis possible to provide for a substantial amount of cooling air flowalong the normally hot leading edge of the blade.

Other objects of the invention will become apparent upon reading theannexed detailed description in connection with the drawing in which:

FIG. 1 is an axial sectional view through a gas turbine rotor havingblades embodying the invention;

FIG. 2 is an elevation view of a blade embodying the invention;

FIG. 3 is a side View taken along line 33 of FIG. 2;

FIGS. 4, 5, 6, 7, 8, 9 and 10 are sectional views taken along lines 44,5-5, 6-6, 77, 8-8, 9, 161t} of FIG. 2, respectively;

FIGS. 11 and 12 are elevation views of the inner surface of the twohalves of the blade prior to their assembly;

FIG. 13 is a view similar to FIG. 2 but illustrating a modifiedstructure; and

FIG. 14 is a sectional view taken along line 14-14 of FIG. .13.

Referring first to FIG. 1 of the drawing, a gas turbine rotor has aplurality of circumferentially-spaced blades 12 secured to and extendingfrom the periphery of the disc portion of said rotor across the flowpath of the turbine motive fluid. A shroud 13 forms the outer boundaryof said flow path. For the purpose of supplying cooling air or othercooling fluid to the turbine blades, an annular shroud 14- is co-axiallysecured to :a plurality of bosses 15 projecting axially from the discportion of turbine rotor. The inner edge of the shroud 14 terminatesshort of the hub of the turbine rotor to leave an annular entrance 18for cooling air flow into the space between the shroud 3,fll?,l59Patented Jan. 16, 1962 14 and the turbine rotor. A plurality ofradially-disposed and circumferentially-spaced vanes 19 may be disposedbetween the shroud 14 and the turbine rotor 10 to help blow cooling airfrom said air entrance 18 to the periphery of the turbine rotor disc andthence into the root ends of the turbine rotor blades 12 for flowthrough said blades. The outer edge of the shroud 14 engages flanges 15on the rotor blades 12 and projecting axially upstream therefrom forrestricting said cooling air to flow into the root ends of said bladesas hereinafter described. The structure so far described is largelyconventional and, for example, is more fully illustrated in copendingapplication Serial No. 557,051, filed January 3, 1956, now US. PatentNo. 2,951,340, and the cooling air flow may be regulated in the mannerdescribed in said copending application.

The details of the rotor blades 12 are illustrated in FIGS. 2-12. Ashereinafter described the blade 12 is fabricated in two halves 12a and1212 (see FIGS. 11 and 12) and the junction between said halves isindicated by the line I in FIGS. 3-10. Each blade 12 has a workingportion 211 and a root portion 22. The working portion 20 of the bladehas an airfoil-like shape for co-action with the turbine motive fluidpassing between the blades for driving the turbine. The root portion 22of the blade is adapted for securement to the periphery of the turbinerotor disc. For this purpose, the root portion is illustrated as havingribs 24 formed thereon to form a fir tree shaped root portion arrangedto be received in slots of complementary configuration in the turbinerotor disc. Each blade 12 also has a circumferentially-extending shelf26 between its working or airfoil-like portion and root portion, saidblade shelves being arranged to abut each other to form a continuousannular inner boundary for the turbine motive fluid, the blade airfoilor working portions 21 projecting across the flow path of said motivefluid from their respective shelves 26. The blade shelves 26 aredisposed outwardly of their previously described flanges 15.

A cavity or chamber 28 is formed in the root portion of each bladebetween its shelf 26 and its fir tree configuration 24- and an opening30 in the upstream side of the blade root portion communicates with thiscavity. Each blade opening 31 is disposed on the radially inner side ofits flange 15. The blade flanges 15 form a substantially-continuousaxially-extending annular flange which is engaged by the outer edge ofthe aforedescribed blower shroud 14 for causing the cooling air to flowinto the turbine blade root openings 30.

The working or airfoil portion 20 of each blade also has a hollowconstruction. Thus the Working portion 20 of each blade comprises thinwalls 34 and 36 forming the blade convex and concave faces,respectively, said walls preferably having a tapering thickness so thattheir thickness is a minimum at the outer ends of the blade. In additiona plurality of webs or partitions 38 extend across the hollow interiorof the blade from one blade face to the other to divide said hollowblade interior into a plurality of passages 40. As hereinafterdescribed, each web 38 comprises a part 384 formed integral with convexblade face 3 1 and a part 38b formed integral with the concave bladeface 36, said web parts abutting and being joined together when theblade halves are joined. At the root end of the blade working portion,the webs 33 3 are spaced chordwise across the blade and said webs extendlengthwise of the blade from its root end for varying distances and thenturn chordwise across the blade to its trailing edge 42. The web 38,disposed adjacent to the leading edge 44 of the blade, extends forsubstantially the entire length of the blade while the lengthwise extentof each of the other webs 38 progressively decreases chordwise acrossthe blade so that the web 33 disposed adjacent to the trailing edge 42of the blade has the shortest dimension lengthwise of the blade.

A narrow slot is formed along the trailing edge of each blade and theWebs 38 terminate at said slot 45 so that the portion 46 of said slotbetween each adjacent pair of webs 38 forms a restricted dischargeopening or orifice 46 for the passage 44) formed by said pair of webs.

At the blade root portion the webs 38 extend into the root portioncavity or chamber 28 but each web separates into two spaced ribs 38a and38b each formed on one face of the blade and each progressivelydecreasing in height as it extends farther into said cavity so that theroot end of each said rib blends into the adjacent outer wall of theblade. With this arrangement, the cavity or chamber 28 in the rootportion of the blade is in communication with each of the blade passages4% so that cooling air supplied to said cavity through the opening 39flows through the passages 40 and discharges from the trailing edge ofthe blade through the restricted openings 46.

A web 48 extends chordwise across the blade working portion at its outerend to close said end in order that cooling air cannot dischargeradially from the outer end of the blade. Also one or more shortchordwise extending webs 5t) divide the chordwise portion of certain ofthe passages 4h into a plurality of parallel passages to help distributethe cooling air across said passages 40.

With the aforedescribed construction, the airflow through the blade iscontrolled by the restricted openings 46 disposed along the bladetrailing edge 42 for each of the passages 46 so that said restrictedopenings 46 control the airflow distribution through the blade.Accordingly, the passages 40, with their restricted discharge openings46, can be designed to provide any desired airflow distribution throughthe blade which distribution Will be unaifected by change in operatingconditions of the turbine. This is in contrast to hollow blades havingpassages discharging air at the outer end of the blade since thereobviously is a different pressure variation on the concave and convexfaces of the airfoil and there is a pressure gradient chordwise acrossthe outer end of a turbine blade, said pressures changing with changesin the operating conditions of the turbine. In addition, with airdischarging from the outer end of a blade the air flow distribution inthe blade will be affected by the small clearance between the blade andthe adjacent stator wall which clearance is difficult to controlaccurately.

Because of the restricted openings 46, the cooling air discharges atrelatively high velocity from the trailing edge of the blade. Thetrailing edge of a turbine blade normally runs hot. The high velocityflow'of the cooling air through the restricted openings in-provides forhigh heat transfer from the adjacent Portions of the blade therebyeffectively cooling'the blade trailing edge.

The leading edge of a turbine blade is the other region of such a bladewhich normally runs hot and therefore like the trailing edge requiresmore effective cooling than the portions of the blade between its saidleading and trailing edges. In order to efiectively cool the leadingedge of the blade 12 the restricted openings 46 along the trailing edgeare designed to provide for a relatively large amount of air flowthrough the passage 40 disposed along said leading edge. For thispurpose, the length of the discharge opening 46, as measured along theblade trailing edge 42, for the leading edge passage 40 is relativelylong compared to the discharge openings 46 for the other passages 49whereby the area of the restricted opening 46 for said leading edgepassage 4% is relatively large.

The temperature distribution pattern of the turbine motive fluid usuallyis such that the highest temperatures occur midway along the blade. Toincrease the cooling midway along the leading edge 44 of the blade 12the passage as along said leading edge converges slightly in this regionas indicated at 52 thereby increasing the velocity of the cooling airflow and hence the cooling in this region.

in order to fabricate a blade 12, it is made in two halves 12a and 1212as previously mentioned and as best seen in FIGS. 11 and 12. The bladehalf 12a includes the convex face 34 with part of the leading andtrailing edges of the blade working or airfoil portion and the majorportion 22a of the blade root. In addition rib portions or halves 38a,48a and 50a of the Webs 38, 48 and 50' respectively are formed integralwith the blade half 1212. Likewise the blade half 1211 includes the concave face 36 with remaining part of the leading and trailing edges ofthe blade working portion and the remaining portion 22b of the bladeroot. Also the other rib portions or halves 38b, 48b and 50b of the Webs38, 43 and 50, respectively, are formed integral with their blade half12b. The rib halves 33a and 38b as well as the other of said rib halvesall abut each other so that the portion of the junction I between theleading and trailing edges of the blades is defined by the abuttingsurfaces of said ribs.

Each blade half 12a and 12b preferably is a precision casting and thesurfaces of each blade half to be joined to the complementary or matingsurfaces of the other blade half are machined to provide an accurate fitwith the other blade half. The shape and position of the mating surfacejunction J of the two halves is shown in FIGS. 310 and is so chosen thatmating surfaces can be machined by a straight line pass of the cutterwithout any relative twisting of the blade or cutter. In other words themating surface junction J of each blade half 12a and 12b is acylindrical surface, although as illustrated, not necessarily a circularcylindrical surface, in that it can be defined by a straight line movingparallel to itself. In the blade illustrated the generating line of saidcylindrical mating surface I is inclined to the longitudinal axis of theblade. The two blade halves are then brazed together at their matingsurfaces. Following the brazing operation the fir treeribs 24 and theshelf portions of the blade root are accurately machined. The trailingedge portions of the two blade halves are formed so as to pro vide thetrailing edge slots 46 when the two halves are brazed together.

It is known that the heat transfer efficiency of a plurality of shortwebs is substantially better than that of a single long web having thesame length as the combined length of the short webs. The heat transferefiiciency increases as the length of the webs along the flow path isdecreased so that a short web having the shape of a pintype projectionhas even superior heat transfer properties. Accordingly it is within thescope of the invention to add and/or substitute a plurality of shortwebs and/or pin-type projections within the airfoil portion of thehollow blade. Such a modification, illustrated in FIGS. 13 and 14,although superior from the standpoint of the cooling effectiveness ofthe air flowing through the blade is more complex from a fabricationstandpoint. For ease of understanding the parts of FIGS. 13 and 14corresponding to parts of FIGS. 1 12, have been designated by the samebut primed reference numerals. 7

Referring to FIGS. 13 and 14 at least one of the lengthwise extendingwebs has been eliminated to widen the leading edge passage 40 and aplurality of pin-type projections of circular cross-section are spacedalong the leading edge portion of this passage and along a portion ofthe adjacent passage in order to increase the cooling effectiveness ofthe cooling airflowing through said passages. Each of the projections 60comprises two parts 60a and 60b. The parts 60a and 60b of eachprojection 60 are formed integral with the convex and concave bladefaces 34' and 36' respectively with each part extending part way acrossits hollow blade passage into abutting engagement with the other part ofits projection 60.

A plurality of relatively short webs 62 are spaced along the chordwiseportions of the various blade passages 40' in the region of the trailinghalf of the blade to increase the cooling effectiveness of the air inthis portion of the blade. For this purpose certain of the chordwisewebs 50 have been replaced by a plurality of 'short chordwise extendingwebs 62 and other webs 62 have been added. Short webs 62 are used alongthe trailing half of the blade instead of the pin-type projectionsbecause this half of the blade is relatively thin. Thus if pins 60 wereused in this thin portion of the blade then because of the large filletsdesired at the junction of each pin with its blade face the averagewidth of each pin would be much greater in this thin portion of theblade.

Each of the webs 62 comprises two short ribs 62a and 62b. The ribs 62aand 62b are formed integral with the convex and concave blade faces 34'and 36' respectively with each rib extending part way across its hollowblade passage into abutting engagement with the other rib of its web 62.

The two parts 60a and 60b of each pin type projection 60 and the twoparts 62a and 62b of each short web 62, like the halves of the variousribs between the blade faces, all abut each other along theaforementioned junction J.

While we have described our invention in detail in its present preferredembodiment, it will be obvious to those skilled in the art, afterunderstanding our invention, that various changes and modifications maybe made therein without departing from theh spirit or scope thereof. Weaim in the appended claims to cover all such modifications.

We claim as our invention:

1. A rotor blade for turbines, compressors or the like; said bladehaving a hollow airfoil portion and a root portion, said root portionhaving a cavity therein and an opening for the supply of a heat exchangefluid to said cavity for flow therefrom through said blade airfoilportion, said airfoil portion having opposed faces extending lengthwiseof the blade and leading and trailing edges also extending lengthwise ofthe blade and joining said faces, said blade airfoil portion also havinga plurality of spaced partitions dividing the hollow interior of saidairfoil portion into a plurality of passages communicating at one endwith said root portion cavity such that all of said heat exchange fluidflowing through said airfoil portion flows through said passages, saidpassages being spaced chordwise across the blade airfoil portionadjacent to the root portion of the blade and all of said passagesextending lengthwise of the blade from the blade root portion but forvarying distances and then turning toward and terminating in individualdischarge openings spaced along the trailing edge of the blade airfoilportion, the passage adjacent to the leading edge of the blade airfoilportion extending lengthwise substantially the entire length of theblade airfoil portion and the lengthwise extent of the other of saidpassages progressively decreasing chordwise across the blade airfoilportion so that the passage adjacent to the blade trailing edge has itsdischarge opening disposed adjacent to the blade root portion and sothat the discharge openings of said passages are disposed alongsubstantially the entire length of said trailing edge, each of saidpassages having a restriction at its discharge opening and said leadingedge passage having a reduced area region in its leading edge portionand disposed approximately midway along the blade leading edge.

2. A rotor blade for turbines, compressors or the like; said bladehaving a hollow airfoil portion and a root portion, said root portionhaving a cavity therein and an opening for the supply of a heat exchangefluid to said cavity for flow therefrom through said blade airfoilportion, said airfoil portion having opposed faces extending lengthwiseof the blade and leading and trailing edges also extending lengthwise ofthe blade and joining said faces, said blade airfoil portion also havinga plurality of spaced partitions dividing the hollow interior of saidairfoil portion into a plurality of passages communicating at one endwith said root portion cavity such that all of said heat exchange fluidflowing through said airfoil portion flows through said passages, saidpassages being spaced chordwise across the blade airfoil portionadjacent to the root portion of the blade and all of said passagesextending lengthwise of the blade from the blade root portion but forvarying distances and then turning toward and terminating in individualdischarge openings spaced along the trailing edge of the blade airfoilportion, the passage adjacent to the leading edge of the blade airfoilportion extending lengthwise substantially the en tire length of theblade airfoil portion and the lengthwise extent of the other of saidpassages progressively decreasing chordwise across the blade airfoilportion so that the passage adjacent to the blade trailing edge has itsdischarge opening disposed adjacent to the blade root portion and sothat the discharge openings of said passages are disposed alongsubstantially the entire length of said trailing edge, said blade havinga narrow slot formed along the blade trailing edge and the bladepartitions, separating the blade passages, terminating at said slot sothat each portion of said slot between a pair of adjacent partitionsforms the restricted discharge opening for the passage formed by saidpair of partitions.

3. A rotor blade for turbines, compressors or the like; said bladehaving a hollow airfoil portion and a root portion, said root portionhaving a cavity therein and an opening for the supply of a heat exchangefluid to said cavity for flow therefrom through said bladeairfoil'portion, said airfoil portion having opposed faces extendinglengthwise of the blade and leading and trailing edges also extendinglengthwise of the blade and joining said faces, said blade airfoilportion also having a plurality of spaced partitions dividing the hollowinterior of said airfoil portion into a plurality of passagescommunicating at one end with said root portion cavity such that all ofsaid heat exchange fluid flowing through said airfoil portion flowsthrough said passages, said passages being spaced chordwise across theblade airfoil portion adjacent to the root portion of the blade and allof said passages extending lengthwise of the blade from the blade rootportion but for varying distances and then turning toward andterminating in individual discharge openings spaced along the trailingedge of the blade airfoil portion, the passage adjacent to the leadingedge of the blade airfoil portion extending lengthwise substantially theentire length of the blade airfoil portion and the lengthwise extent ofthe other of said passages progressively decreasing chordwise across theblade airfoil portion so that the passage adjacent to the blade trailingedge has its discharge opening disposed adjacent to the blade rootportion and so that the discharge openings of said passages are disposedalong substantially the entire length of said trailing edge, the leadingedge portion of the blade leading edge passage having a plurality ofcylindrical projections spaced along and extending across said leadingedge passage portion and the trailing edge portions of at least some ofthe blade passages having a plurality of short webs spaced along andextending across said trailing edge passage portions with the sides ofeach web being disposed substantially parallel to the sides of itspassage, each of said cylindrical projections and webs being formedintegral with at least one of the faces of the blade airfoil portion.

(References on following page) References Cited in the file of thispatent UNITED STATES PATENTS Kane Apr. 24, 1951 Williams June 9, 1953Cangerni July 7, 1953 Tn'ebbnigg Aug. 4, 1953 Kempe June 1, 1954 SmithAug. 24, 1954 Daugherty Jan. 18, 1955 Williams Jan. 25, 1955 8 RoushSept. 24, 1957 H011 Dec. 30, 1958 FOREIGN PATENTS Switzerland May 1,1942 Switzerland July 16, 1943 Switzerland Sept. 1, 1953 Great BritainAug. 2, 1950 Great Britain May 11, 1955 Great Britain Dec. 7, 1955 GreatBritain Aug. 8, 1956 Germany Dec. 4, 1952

